1. Field of the Invention
The present invention relates to a wholly aromatic polyamide resin composition having an enhanced light resistance. More particularly, the present invention relates to a wholly aromatic polyamide resin composition comprising a light-resisting compound having at least one naphthalene ring structure and terminal-blocking amide groups and an enhanced light resistance.
2. Description of the Related Art
Wholly aromatic polyamide (aramid) resins have high mechanical strength, a superior modulus and excellent heat resistance and thus are widely useful as fiber and film-forming materials.
Nevertheless, it is well known that conventional wholly aromatic polyamide resins are disadvantageous in that they have poor light-resistance.
Japanese Unexamined Patent Publication No. 49-100,322 discloses a method of enhancing the light resistance of the conventional wholly aromatic polyamide resins by adding a benzotriazol type ultraviolet ray-absorbing agent and an antioxidant to a dope solution of a poly-m-phenylene isophthalamide resin in N-methylpyrrolidone. However, the light resistance-enhancing effect of this method is not satisfactory.
It is known that poly-p-phenylene terephthalamide (PPTA) resin does not easily melt and dissolve in a usual organic solvent, and can be shaped only by dissolving the PPTA resin in a special solvent, for example, sulfuric acid and then shaping the resultant dope solution.
The PPTA resin is different from usual fusible resins in that when an additive is mixed with a dope solution of the resin so as to impart a certain function to the resin, the additive must be stable in the special solvent such as sulfuric acid Accordingly, the additive usable for the PPTA. resins is restricted to those stable in the sulfuric acid solvent
For example, Japanese Unexamined Patent Publication No. 64-85,316 discloses the addition of a carbon black to the PPTA resins. Also, Japanese Unexamined Patent Publication No. 64-14,317 discloses the addition of an organic pigment to the PPTA resins to enhance the light resistance thereof. However, the use of the carbon black and organic pigment colors the resultant shaped article, for example, fibers, to a particular shade. Namely, the shade of the resultant colored article is restricted to the specific color. Also, this addition of the carbon black or the organic pigment is disadvantageous in that it is difficult to uniformly disperse the carbon black or the organic pigment in the PPTA resin and the resultant shaped article, for example, fibers, exhibits unsatisfactory mechanical strength.
Further, in a usual method of producing a shaped article, for example, fibers, from a dope solution of an aramid resin mixed with an ultraviolet ray-absorbing agent, the resultant shaped article is usually drawn and/or heat treated at a high temperature, for example, 400.degree. C. to 600.degree. C. This high temperature drawing or heat-treating procedure causes the ultraviolet ray-absorbing agent to chemically decompose and thus the resultant shaped article exhibits substantially no ultraviolet ray-absorbing effect.
Furthermore, it is known that after shaping an aramid resin, it is very difficult to introduce and fix an additive to the shaped aramid resin article, because of high crystallinity and a high intermolecular chain force of the aramid resin.
To overcome this difficulty, Japanese Unexamined Patent Publication Nos. 49-75,824, 50-12,322, 53-35,020 and 1-240,533 and Japanese Examined Patent Publication No. 56-33,487 discloses a method of enhancing the light resistance of aramide fibers by impregnating water-swollen, undried aramide fibers with an ultraviolet ray-absorbing agent. This method, however, is disadvantageous in that impregnation with the additive disturbs the molecular chain structure of the aramid resin fibers and thus the mechanical properties thereof, for example, mechanical strength, are reduced. It is known that a blend of an aramid resin with a wholly aromatic polyamide having a naphthalene ring structure is usable for producing shaped articles, for example, fibers.
For example, Japanese Unexamined Patent Publication No. 62-263,320 discloses aramid fibers made from a blend of an aromatic copolyamide prepared by using a naphthalene ring structure-containing monomer with a poly-p-phenyleneterephthalamide. Also, Japanese Unexamined Patent Publication No. 3-143,922, Example 8, discloses aramid fibers prepared from a blend of a dope solution of a wholly aromatic polyamide having a naphthalene ring structure with a dope solution of another wholly aromatic polyamide resin free from the naphthalene ring structure.
These prior art references are effective for enhancing the mechanical strength of the resultant aramid fibers. Generally, organic polymers having a plurality of functional groups, for example, an amino group and a carboxyl group easily deteriorate or and discolored by a photo-decomposition.
These prior art references do not disclose or suggest block terminals of a naphthalene ring structure-containing a wholly aromatic polyamide molecule.
Also, Japanese Unexamined Patent Publication No. 63-75,111 discloses aramid fibers made from an aramid resin having a 2,6-naphthalamide structure. This 2,6 -naphthalamide structure is introduced into the aramid resin by way of copolymerization of a 2,6-naphthalene ring structure-containing monomer. Namely, this Japanese publication does not disclose or suggest connecting terminal groups of the aramid molecules to non-reactive terminal groups.